1. Field of the Invention
The invention relates to antiperspirant compositions in the form of gelled sticks.
2. The Related Art
Cosmetic sticks which exhibit a clear appearance can be prepared using sodium stearate as a gelling agent or structurant. Unfortunately, these clear sticks cannot be formulated with antiperspirant-active salts because the alkaline gelling agents will react with the acidic salts. This incompatibility has been surmounted through use of neutral structurants, for instance, use of low melting waxy materials such as stearyl alcohol. Stability is good but the resultant sticks are opaque.
For many years, the art has investigated a unique gelling agent known as dibenzyl monosorbitol acetal (DBMSA) for use in translucent or transparent sticks. No derivative of sorbitol or any other gelling agent has yet been found which equals its structurant properties. However, it is also known that acetals are stable only in alkaline or neutral media, but not in acidic media. Under an acidic environment even in the presence of small amounts of water, the acetal hydrolyzes or will react with alcohol, e.g. ethanol, to form a different acetal.
Thus, antiperspirant sticks containing acidic antiperspirant-active salts in the presence of DBMSA in reactive alcoholic solvents have not been satisfactory because, in time, especially at elevated temperatures, they deteriorate and liquify. There is a need, therefore, to find a way to stabilize these sticks against such deterioration.
Antiperspirant sticks containing dibenzyl monosorbitol acetal and antiperspirant-active salts are disclosed in U.S. Pat. No. 4,154,816 (Roehl et al.). These sticks contain, in addition to the antiperspirant-active salt and DBMSA, a lower monohydric alcohol, a di- or trihydric alcohol, a propylene-/ethylene-glycol polycondensate, and optionally an alkylolamide. A problem with these products is their stickiness on application. U.S. Pat. No. 4,346,079 (Roehl) reports elimination or significant reduction of the stickiness problem through replacement of at least part of the polycondensate with an oleaginous compound.
U.S. Pat. No. 4,518,582 (Schamper et al.) found that the Roehl antiperspirant sticks, even with the improved stickiness control, were not stable on extended exposure at elevated temperatures. The problem was addressed through use of a gel stabilizer such as magnesium sulfate, zinc acetate and hexamethylenetetramine. Another remedy for stickiness is disclosed in U.S. Pat. No. 4,720,381 (Schamper et al.) wherein non-reactive solvents were used to replace reactive ones. Less reactive alcohols were identified as isopropanol, isobutanol, dipropylene glycol and other higher molecular weight alcohols. A still further approach was described in U.S. Pat. No. 4,725,430 (Schamper et al.) wherein N-(2-hydroxyethyl) acetamide was utilized as a stabilizing agent in the gel.
Another refinement of the DBMSA system is reported in U.S. Pat. No. 4,781,917 (Luebbe et al.) which utilizes a coupling agent and buffering adjustment agent to improve the stick. The coupling agent may be a polypropylene glycol (PPG) ether of a C.sub.4 -C.sub.22 fatty alcohol. Suitable buffering adjustment agents were stated to be coconut monoethanolamide, sodium aluminum chlorohydroxylactate, sodium hydroxide, stearamide monoethanolamide, acetamide MEA, zinc acetate, zinc oxide, zinc stearate, zinc carbonate and similar materials.
U.S. Pat. No. 4,743,444 (McCall) describes improvements in gel rheology and transparency, while maintaining hardness and physical integrity. These benefits were obtained by incorporation of a C.sub.14 -C.sub.16 fatty alcohol.
U.S. Pat. No. 4,719,102 (Randhawa et al.) in conjunction with a DBMSA gel stick describes novel solvents for use therein to allow processing at lower temperatures. The novel solvent is a compound having not greater than about five carbon atoms that includes, for instance, morpholine, pyridine, acetic acid, ethylene carbonate, propylene carbonate, etc.
EP 0 512 770 A1 (Benfatto et al.) describes DBMSA compositions wherein water and lower monohydric alcohols have been replaced with dihydroxy aliphatic alcohols containing 3 to 6 carbon atoms as solvents.
Westwood Chemical Corporation in its data sheets has suggested that a DBMSA gel stick could be stabilized with zinc glycinate. At higher temperatures this technology is insufficiently effective to prevent cloudiness arising in the gel stick. Clarity is especially adversely effected when the compositions contain emollients necessary to improve product aesthetics and avoid the tacky feel associated with this type of formulation.
Accordingly, it is an object of the present invention to provide an antiperspirant stick gelled with DBMSA which does not deteriorate or become sticky, even at higher temperatures.
Another object of the present invention is to provide an antiperspirant stick gelled with DBMSA that not only is stable but has good clarity, i.e. at least translucent if not transparent.
Still another object of the present invention is to provide an antiperspirant stick gelled with DBMSA that includes emollients yet minimizes the tacky feel commonly associated with these types of formulations.
These and other objects of the present invention will become more readily apparent from consideration of the following summary, examples and detailed description.